MySQL入门

具体内容，请参考MySQL官方文档http://dev.mysql.com/doc/refman/5.5/en/sql-syntax.html

常见的数据库语言主要分以下几类

1. 数据定义语言DDL（Data Definition Language）包括CREATE、ALTER、DROP、TRUNCATE

2. 数据操作语言DML（Data Manipulation Language）包括INSERT、UPDATE、DELETE

3. 数据查询语言DQL（Data Query Language）包括SELECT

4. 数据控制语言DCL（Data Control Language）包括GRANT、REVOKE、DENY

5. 事务控制语言TCL（Transaction Control Language）包括SAVEPOINT、ROLLBACK、COMMIT

一、数据定义语言

找出当前服务器上有哪些数据库：

/*查看服务器上的数据库*/
SHOW DATABASES;

1）创建数据库

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
    [create_specification [, create_specification] ...]
 
create_specification:
    [DEFAULT] CHARACTER SET charset_name
  | [DEFAULT] COLLATE collation_name

/*创建数据库mydb，以分号结尾*/
CREATE DATABASE IF NOT EXISTS mydb;
/*访问数据库mydb，结尾可以不要分号*/
USE mydb

2）创建数据表

/*创建数据表，此处只列举部分参数，完整参数请查阅MySQL官方文档*/
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options] [select_statement]
create_definition:
    column_definition
  | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)
  | KEY [index_name] [index_type] (index_col_name,...)
  | INDEX [index_name] [index_type] (index_col_name,...)
  | [CONSTRAINT [symbol]] UNIQUE [INDEX]
        [index_name] [index_type] (index_col_name,...)
  | [FULLTEXT|SPATIAL] [INDEX] [index_name] (index_col_name,...)
  | [CONSTRAINT [symbol]] FOREIGN KEY
        [index_name] (index_col_name,...) [reference_definition]
  | CHECK (expr)
 
column_definition:
    col_name type [NOT NULL | NULL] [DEFAULT default_value]
        [AUTO_INCREMENT] [UNIQUE [KEY] | [PRIMARY] KEY]
        [COMMENT 'string'] [reference_definition]
 
type:
    TINYINT[(length)] [UNSIGNED] [ZEROFILL]
  | SMALLINT[(length)] [UNSIGNED] [ZEROFILL]
  | MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL]
  | INT[(length)] [UNSIGNED] [ZEROFILL]
  | INTEGER[(length)] [UNSIGNED] [ZEROFILL]
  | BIGINT[(length)] [UNSIGNED] [ZEROFILL]
  | REAL[(length,decimals)] [UNSIGNED] [ZEROFILL]
  | DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL]
  | FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL]
  | DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL]
  | NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL]
  | DATE
  | TIME
  | TIMESTAMP
  | DATETIME
  | CHAR(length) [BINARY | ASCII | UNICODE]
  | VARCHAR(length) [BINARY]
  | TINYBLOB
  | BLOB
  | MEDIUMBLOB
  | LONGBLOB
  | TINYTEXT [BINARY]
  | TEXT [BINARY]
  | MEDIUMTEXT [BINARY]
  | LONGTEXT [BINARY]
  | ENUM(value1,value2,value3,...)
  | SET(value1,value2,value3,...)
  | spatial_type

/*查看正访问数据库的数据表*/
SHOW TABLES;
/*创建数据表users*/
CREATE TABLE IF NOT EXISTS users(
	u_id MEDIUMINT(8),
	u_name VARCHAR(255),
	u_sex TINYINT(3),
	u_phone VARCHAR(11),
	u_address VARCHAR(255)
) ENGINE=MyISAM;

3）删除数据表

/*sql语句格式，可以同时删除多个表*/
DROP [TEMPORARY] TABLE [IF EXISTS]
    tbl_name [, tbl_name] ...
    [RESTRICT | CASCADE]

/*删除users数据表*/
DROP TABLE IF EXISTS users;

4）清空数据表

该操作会清空数据表，同时重新设置AUTO_INCREMENT计数器，效率比DELETE FROM高

TRUNCATE [TABLE] tbl_name

5）修改数据表

/*语言格式*/
ALTER [IGNORE] TABLE tbl_name
    alter_specification [, alter_specification] ...

alter_specification:
    ADD [COLUMN] column_definition [FIRST | AFTER col_name ]
  | ADD [COLUMN] (column_definition,...)
  | ADD INDEX [index_name] [index_type] (index_col_name,...)
  | ADD [CONSTRAINT [symbol]]
        PRIMARY KEY [index_type] (index_col_name,...)
  | ADD [CONSTRAINT [symbol]]
        UNIQUE [index_name] [index_type] (index_col_name,...)
  | ADD [FULLTEXT|SPATIAL] [index_name] (index_col_name,...)
  | ADD [CONSTRAINT [symbol]]
        FOREIGN KEY [index_name] (index_col_name,...)
        [reference_definition]
  | ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
  | CHANGE [COLUMN] old_col_name column_definition
        [FIRST|AFTER col_name]
  | MODIFY [COLUMN] column_definition [FIRST | AFTER col_name]
  | DROP [COLUMN] col_name
  | DROP PRIMARY KEY
  | DROP INDEX index_name
  | DROP FOREIGN KEY fk_symbol
  | DISABLE KEYS
  | ENABLE KEYS
  | RENAME [TO] new_tbl_name
  | ORDER BY col_name
  | CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]
  | [DEFAULT] CHARACTER SET charset_name [COLLATE collation_name]
  | DISCARD TABLESPACE
  | IMPORT TABLESPACE
  | table_options
  | partition_options
  | ADD PARTITION partition_definition
  | DROP PARTITION partition_names
  | COALESCE PARTITION number
  | REORGANIZE PARTITION partition_names INTO (partition_definitions)
  | ANALYZE PARTITION partition_names
  | CHECK PARTITION partition_names
  | OPTIMIZE PARTITION partition_names
  | REBUILD PARTITION partition_names
  | REPAIR PARTITION partition_names

/*查看表的描述*/
DESC table_name;

二、数据操作语言

1）插入数据

/*格式*/
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
    [INTO] tbl_name [(col_name,...)]
    VALUES ({expr | DEFAULT},...),(...),...
    [ ON DUPLICATE KEY UPDATE col_name=expr, ... ]

2）更新数据

/*单表语法*/
UPDATE [LOW_PRIORITY] [IGNORE] tbl_name
    SET col_name1=expr1 [, col_name2=expr2 ...]
    [WHERE where_definition]
    [ORDER BY ...]
    [LIMIT row_count]
/*多表语法*/
UPDATE [LOW_PRIORITY] [IGNORE] table_references
    SET col_name1=expr1 [, col_name2=expr2 ...]
    [WHERE where_definition]

table_references:
    table_reference [, table_reference] …

table_reference:
    table_factor
  | join_table

table_factor:
    tbl_name [[AS] alias]
        [{USE|IGNORE|FORCE} INDEX (key_list)]
  | ( table_references )
  | { OJ table_reference LEFT OUTER JOIN table_reference
        ON conditional_expr }

join_table:
    table_reference [INNER | CROSS] JOIN table_factor [join_condition]
  | table_reference STRAIGHT_JOIN table_factor
  | table_reference STRAIGHT_JOIN table_factor ON condition
  | table_reference LEFT [OUTER] JOIN table_reference join_condition
  | table_reference NATURAL [LEFT [OUTER]] JOIN table_factor
  | table_reference RIGHT [OUTER] JOIN table_reference join_condition
  | table_reference NATURAL [RIGHT [OUTER]] JOIN table_factor

join_condition:
    ON conditional_expr
  | USING (column_list)

3）删除数据

/*单表语法*/
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
    [WHERE where_definition]
    [ORDER BY ...]
    [LIMIT row_count]
/*多表语法*/
DELETE [LOW_PRIORITY] [QUICK] [IGNORE]
    tbl_name[.*] [, tbl_name[.*] ...]
    FROM table_references
    [WHERE where_definition]

/*当搜索待删除的行时，这些语句使用所有三个表，但是只从表t1和表t2中删除对应的行*/
DELETE t1, t2 FROM t1, t2, t3 WHERE t1.id=t2.id AND t2.id=t3.id;